Glass Precursor Gel

ABSTRACT

A glass precursor gel and a method of making a glass product from the glass precursor gel are disclosed. The glass precursor gel includes a bulk amorphous oxide-based matrix that is homogeneously chemically mixed and includes 30 mol % to 90 wt. % silica and at least one of the following: (A) 0.1 mol % to 25 mol % of one or more alkali oxides in sum total, (B) 0.1 mol % to 25 mol % of one or more alkaline earth oxides in sum total, (C) 1 mol % to 20 mol % boric oxide, (D) 5 mol % to 80 mol % lead oxide, or (E) 0.1 mol % to 10 mol % aluminum oxide. A method of making a glass product from the glass precursor gel involves obtaining the glass precursor gel, melting the glass precursor gel into molten glass, and forming the molten glass into a glass product.

The present disclosure is directed to a glass precursor gel for makingglass products and, more particularly, to a glass precursor gel thatrapidly converts into molten glass when heated.

BACKGROUND AND SUMMARY OF THE DISCLOSURE

Glass products have long been made from a pre-formulated feedstock (alsosometimes termed a glass batch) that is charged into a glass furnace andmelted to produce molten glass for subsequent formation into the desiredglass product. A typical feedstock includes a physical mixture of virginraw materials and, optionally, recycled glass materials known in theindustry as “cullet.” The virgin raw materials contain quartz sand(crystalline SiO₂) and other ingredients, such as soda ash (Na₂CO₃) andlimestone (CaCO₃) for soda-lime-silica glass, for example, and thecullet primarily contains shards of glass from previously-formedconsumer or commercial glass products. The cullet component of thefeedstock can vary based on the glass-forming process being practicedand the desired characteristics of the final glass product (e.g., color,transparency, etc). In many instances, however, the feedstock maycontain up to about 80 weight percent cullet, with the remainder beingvirgin raw materials which may or may not include, in addition to theingredients listed above, a small percentage of other ingredientsincluding glass network formers, network modifiers, colorants,decolorants, fining agents, and redox agents, to name but a few.

The residence time of the conventional glass feedstock in the glassfurnace is relatively long. This can be attributed to several factors.First, the largest component of the virgin raw materials, quartz sand,and usually some of the other virgin raw material ingredients—e.g., sodaash and limestone for soda-lime-silica glass—are crystalline materials.Their crystal structures, including intermediate crystalline phases, aregenerally present up to about 1200° C., as melting and dissolution ofthese materials does not occur instantaneously. Second, the glassfeedstock needs to be dispersed and homogeneously mixed by convectionafter being melted to produce molten glass, which is a time-consumingprocess. Quartz sand, in particular, takes the longest disperse onaccount of its slow dissolution rate and the tendency to agglomerateinto SiO₂-rich regions within the glass melt known as “cord.” Thepresence of cord is indicative of glass inhomogeneity and may result inimperfections or defects in the finished glass product. Third, some ofthe virgin raw material ingredients—e.g., soda ash and limestone forsoda-lime-silica glass—are carbonate-containing materials that, whenmelted, release carbon dioxide (CO₂). The evolution of carbon dioxideduring feedstock melting introduces bubbles in the resultant moltenglass, which, in turn, can cause a thin spot or bubble defect in thefinished glass product. Any such bubbles are typically removed from themolten glass in a process known as “refining the glass.” To address thechallenges associated with melting and homogenizing crystalline rawmaterials and to remove bubbles caused by carbon dioxide evolution,among other factors, conventional glass feedstocks are usually subjectedto high temperatures and heating times of 24 hours or more in the glassfurnace in order to obtain suitably-refined and chemically homogenizedmolten glass.

The melting of the glass feedstock can be made less taxing if some ofthe virgin raw materials are replaced with cullet in the feedstock. Thecullet accelerates the melting of the feedstock and lowers furnaceenergy consumption as compared to a feedstock that contains all virginraw materials. Cullet has this effect because it has already beenmelted, mixed, and formed into a glass product and will not releasecarbon dioxide when re-melted since it is not an intrinsiccarbonate-containing material. But cullet is not widely available as acommodity in some regions and, even if it is, bulk purchases of therecycled material are subject to great variations in color and othercharacteristics that may restrict glass manufacturing options.Post-consumer cullet also has the tendency to be contaminated withmetals, glues, and other organics, and is sometimes difficult touniformly mix with virgin raw materials in the glass furnace whenmelted. Moreover, even with the addition of cullet, current glassmanufacturing practices still typically involve melting the glassfeedstock and homogenizing/refining the molten glass in the glassfurnace at a temperature of around 1400° C. or higher for at least about24 hours. Such long processing times at elevated temperatures require alot of energy and slow the overall glass-making process.

One or more embodiments set forth in the present disclosure may achieveany of a variety of objectives including, for example, obtaining a glassprecursor gel that can be melted without requiring long residence timesin the glass furnace in order to achieve homogeneous and refined moltenglass. The glass precursor gel has a bulk amorphous oxide-based matrixthat includes a homogeneous chemical mixture of the primary constituentoxides and any secondary materials, in the proportions desired, of thefinal glass product composition. Moreover, when the glass precursor gelis heated and melted, it releases no more than a negligible amountcarbon dioxide due to the fact that it does not include carbonates.Because the glass precursor gel includes an already homogenous chemicalmixture of the primary constituent oxides, as well as relatively smallamounts of any other secondary materials, and because it does notcontain carbonates, it does not require a lengthy refining process;rather, it only needs to be heated for a relatively short period of timeto obtain a homogeneous and bubble-free molten glass that is ready fordownstream production into a glass product.

The present disclosure embodies a number of aspects that can beimplemented separately from or in combination with each other.

In accordance with one aspect of the present disclosure, there isprovided a glass precursor gel that comprises a bulk amorphousoxide-based matrix. The amorphous oxide-based matrix is homogeneouslychemically mixed and includes 30 mol % to 90 mol % silica and at leastone of the following: (A) 0.1 mol % to 25 mol % of one or more alkalioxides (mol % is the sum total), (B) 0.1 mol % to 25 mol % of one ormore alkaline earth oxides (mol % is the sum total), (C) 1 mol % to 20mol % boric oxide (B₂O₃), (D) 5 mol % to 80 mol % lead oxide (PbO), or(E) 0.1 mol % to 10 mol % aluminum oxide (Al₂O₃). The glass precursorgel has a density of less than 2.0 g/cm³.

In accordance with another aspect of the disclosure, there is provided amethod of making a glass product. The method includes obtaining a glassprecursor gel that comprises a homogeneously chemically mixed bulkamorphous oxide-based matrix and an extending swelling agent. The bulkamorphous oxide-based matrix has an inorganic network of primaryconstituent oxides. The primary constituent oxides comprise 30 mol % to90 mol % silica and one or more of the following: (A) 0.1 mol % to 25mol % of one or more alkali oxides (mol % is the sum total), (B) 0.1 mol% to 25 mol % of one or more alkaline earth oxides, (C) 1 mol % to 20mol % boric oxide, (D) 5 mol % to 80 mol % lead oxide, or (E) 0.1 mol %to 10 mol % aluminum oxide. The method further includes melting theglass precursor gel into molten glass and forming the molten glass intoa glass product.

In accordance with yet another aspect of the disclosure, there isprovided a method of making a glass product. The method involvesproviding a silicate solution that includes a dissolved sodium silicatecomprising a molar ratio of Na₂O:SiO₂. A soluble calcium salt is addedto the silicate solution to displace some of the sodium oxide in thedissolved sodium silicate with calcium oxide and to derive a wetprecipitate that comprises a molar ratio of Na₂O:CaO:SiO₂. Solvent isthen removed from the wet precipitate to obtain a soda-lime-silica glassprecursor gel that comprises a homogeneously chemically mixed bulkamorphous oxide-based matrix having an inorganic network of 60 mol % to85 mol % silica, 8 mol % to 18 mol % sodium oxide, and 5 mol % to 15 mol% calcium oxide. The soda-lime-silica glass precursor gel is melted intomolten glass which, in turn, is formed into a glass product.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure, together with additional objects, features, advantagesand aspects thereof, will be best understood from the followingdescription, the appended claims and the accompanying drawings, inwhich:

FIG. 1 is a flow diagram that depicts a method of preparing and using aglass precursor gel, in particular a soda-lime-silica glass precursorgel, to form a soda-lime-silica (“SLS”) glass product;

FIG. 2 is a table listing several different possible compositions of thebulk amorphous oxide-based matrix of the glass precursor gel dependingon the desired type of glass sought to be formed; and

FIG. 3 is a graph depicting the % transmittance versus wavelength ofcommercial flint glasses made from conventional soda-lime-glassfeedstocks as well as a flint glass made from the SLS precursor geldiscussed in this disclosure.

DETAILED DESCRIPTION

A glass precursor gel that can be used as an alternative to traditionalglass feedstock mixtures for deriving molten glass is disclosed. Theglass precursor gel comprises a bulk amorphous (i.e., non-crystalline)oxide-based matrix characterized by an inorganic network of at least theprimary constituent oxides of the final glass composition. The primaryconstituent oxides are present in the amorphous oxide-based matrix atthe desired proportions of the final glass composition. Morespecifically, the primary glass-forming constituent oxides included inthe amorphous oxide-based matrix are 30 mol % to 90 mol % silica and oneor more of the following: (A) 0.1 mol % to 25 mol % of one or morealkali oxides (mol % is the sum total); (B) 0.1 mol % to 25 mol % of oneor more alkaline earth oxides (mol % is the sum total); (C) 1 mol % to20 mol % boric oxide (B₂O₃); (D) 5 mol % to 80 mol % lead oxide (PbO),or (E) 0.1 mol % to 10 mol % aluminum oxide (Al₂O₃). The one or morealkali oxides may be selected from the group consisting of lithium oxide(Li₂O), sodium oxide (Na₂O), potassium oxide (K₂O), rubidium oxide(Rb₂O), cesium oxide (Cs₂O), and combinations thereof, and the one ormore alkaline earth oxides may be selected from the group consisting ofmagnesium oxide (MgO), calcium oxide (CaO), strontium oxide (SrO),barium oxide (BaO), and combinations thereof.

In one embodiment, the amorphous oxide-based matrix may include at least60 mol % to 85 mol % silica (SiO₂), 8 mol % to 18 mol % sodium oxide(Na₂O), and 5 mol % to 15 mol % calcium oxide (CaO) as the primaryconstituent oxides, in which case the gel is composed to producesoda-lime-silica glass. In other embodiments, the glass precursor gelmay be composed to produce other types of glass including borosilicateglass and lead sealing glass. Regarding borosilicate glass, theamorphous oxide-based matrix may include at least 30 mol % to 85 mol %silica and 1 mol % to 20 mol % boric oxide, along with at least one of 2mol % to 25 mol % calcium oxide or 2 mol % to 20 mol % sodium oxide, asthe primary constituent oxides depending on the anticipated end-use.Regarding lead sealing glass, the amorphous oxide-based matrix mayinclude at least 30 mol % to 70 mol % silica, 15 mol % to 60 mol % leadoxide, and at least one of 3 mol % to 15 mol % potassium oxide, 2 mol %to 10 mol % sodium oxide, or 4 mol % to 10 mol % boric oxide, as theprimary constituent oxides.

In addition to the primary constituent oxides, the amorphous oxide-basedmatrix may optionally include a number of secondary materials that arecommonly used in the glass manufacturing industry. Examples of suchsecondary materials are up to 25 mol % total of other glassnetwork-formers, up to 2 mol % total of coloring and/or decoloringagents, and up to 20 mol % total of other materials that can affect thephysical properties and/or the redox state of the final glass productcomposition. Specific other glass network-formers that may be addedinclude one or more of phosphorus oxide (P₂O₅) and germanium oxide(GeO₂). Specific colorants and decolorants that may be added include theelemental forms or oxide compound forms of one or more of selenium,chromium, manganese, iron, cobalt, nickel, copper, niobium, molybdenum,silver, cadmium, indium, tin, gold, cerium, praseodymium, neodymium,europium, gadolinium, erbium, and uranium. And specific materials thatcan affect the physical properties and/or the redox state of the glassinclude one or more of carbon (0 mol % to 3 mol %), nitrates (0 mol % to3 mol %), selenium (0 mol % to 1 mol %), titanium oxide (TiO₂) (0 mol %to 5 mol %), arsenic oxide (As₂O₃) (0 mol % to 2 mol %), vanadium oxide(V₂O₅) (0 mol % to 5 mol %), fluorines (0 mol % to 2 mol %), chlorines(0 mol % to 2 mol %), and sulfates (0 mol % to 2 mol %).

The exact composition of the amorphous oxide-based matrix including theproportions of its primary constituent oxides and optional secondarymaterials can be varied to achieve any of the large variety of glasschemistries that may be desired in the final glass product. Both thephysical and chemical properties of the resultant glass derived from theglass precursor gel can be affected by variances in the relativeproportions of the primary constituent oxides as well as the inclusionor exclusion of certain secondary materials in the amorphous oxide-basedmatrix. For example, certain exemplary glass chemistry formulations ofdifferent types of finished glass are enumerated in FIG. 2. Accordingly,in order to derive these types of finished glass from the glassprecursor gel, the amorphous oxide-based matrix can be prepared to havethe same proportions of the primary constituent oxides and secondarymaterials so that, upon melting, a molten glass is obtained that can beformed by standard techniques into the glass product.

Within the amorphous oxide-based matrix, the primary constituent oxidesand any secondary materials, which may or may not be present, arehomogeneously chemically mixed. The term “homogeneously chemicallymixed” and its grammatical variations, as used herein, means thatmultiple different samples of the gel will have the same molepercentages of the three primary constituent oxides present in thegreatest amounts in the amorphous oxide-based matrix. Different samplescan be said to have the same mole percentages of the three primaryconstituent oxides when the mole percent of each primary constituentoxide in each sample lies within a range of ±3% of the arithmeticaverage [i.e., (0.97)(average)<sample<(1.03)(average)] of itsrespective oxide as determined from the various samples taken. Forexample, five random, different samples of a glass precursor gel havebeen found through x-ray fluorescence to have the following molepercentages of the three main primary constituent oxides (here, silica,sodium oxide, and calcium oxide):

TABLE 1 Compositions of Samples Mole Percentage of: Sample # SiO₂ Na₂OCaO 1 72.3 14.2 12.1 2 72.2 14.1 12.2 3 71.8 14.2 12.5 4 72.1 14.1 12.45 72.5 13.9 12.3 Avg. 72.2 14.1 12.3As can be seen, in this group of samples, the arithmetic average ofsilica, sodium oxide, and calcium oxide as determined from the fivesamples is 72.2 mol %, 14.1 mol %, and 12.3 mol %, respectively. Therange of ±3% of the arithmetic average for each of the primaryconstituent oxides can then be calculated as 70.03-74.34 mol % forsilica, 13.68-14.52 mol % for sodium oxide, and 11.93-12.67 mol % forcalcium oxide. The mole percentage of each primary constituent oxide ineach sample clearly falls within those prescribed ranges, and thusconfirms that the amorphous oxide-based matrix of the glass precursorgel is homogeneously chemically mixed.

The amorphous oxide-based matrix is light, porous, and hygroscopic,which allows for an extending swelling agent, such as water, to beentrapped within the inorganic network of oxides. Indeed, water istypically retained in the glass precursor gel at a relatively highamount as compared to cullet. In particular, cullet evolves water vaporup to about 125° C. when heated at a rate of 5° C. per minute startingfrom STP (1 atm pressure and 20° C.), and is thoroughly dried for themost part at 150° C., which is typical of physically entrained water. Onthe other hand, the glass precursor gel continues to evolve watervapor—an additional 1-10 wt. %—above 125° C. and up to 400° C. whensubjected to the same incremental heating, and may even retain as muchas 0.5 wt. % water at 400° C., which is indicative of water that ischemically bound to amorphous oxide-based matrix as a swelling agent.The presence of retained chemically-bound water within the amorphousoxide-based matrix may be advantageous in some instances since it actsas a flux that lowers the processing temperature of molten glass,particularly at low temperatures. And despite the fact that the glassprecursor gel typically includes chemically-entrained water within itsamorphous oxide-based matrix, the glass precursor gel has a density ofless than 2.0 g/cm³, preferably between about 1.6 g/cm³ and about 1.85g/cm³ including all ranges and sub-ranges therebetween, and a surfacearea of at least 20 m²/g, preferably about 25 m²/g to about 40 m²/gincluding all ranges and sub-ranges therebetween, as measured bynitrogen BET adsorption. The glass precursor gel is thus less dense andhas a higher surface area than cullet.

The composition of the glass precursor gel facilitates rapid meltinginto molten glass while avoiding long residence times in the glassfurnace. The glass precursor gel does not include large quantities ofcrystalline materials and, most notably, the amorphous oxide-basedmatrix does not contain any crystalline precursor materials of silicasuch as, for example, quartz sand. The absence of quartz sand isnoteworthy here. Unlike conventional glass feedstocks that contain afair amount of quartz sand, which generally has a slow dissolution rate,the glass precursor gel does not have to be maintained in a molten stateat high temperatures for long durations in order to achieve satisfactorySiO₂ dissolution. The amorphous oxide-based matrix also includesvirtually no carbonate-containing materials and, as such, will produceno more than a negligible amount of CO₂ upon melting and hence no morethan a negligible amount of bubbles within the molten glass. The moltenglass obtained from the glass precursor gel therefore does not have tobe refined by removing substantial amounts of entrained bubbles throughextended heating times. Given that the amorphous oxide-based matrix isalready homogeneously chemically mixed and does not contain crystallineprecursor materials of the primary constituent oxides or more than aninsignificant amount of carbonate-containing materials, the glassprecursor gel does not have to be heated to as high of a temperature ormaintained at an elevated temperatures for as long of a timeframe asconventional glass feedstocks in order to obtain a molten glass that issuitable for downstream processing into a glass product.

To be sure, as mentioned above, conventional soda-lime-silica glassfeedstocks are typically melted in a furnace and maintained at 1400° C.or higher for at least about 24 hours in order to obtain a suitablyrefined and homogenized molten glass. The glass precursor gel set forthin the present disclosure does not require—although it certainly doesnot preclude—such heat cycle demands. The gel, in fact, can be heated toabove its melting temperature for as little as 30 minutes and stillresult in molten glass that is refined, homogenized, and ready forfurther glass processing (e.g., fashioning into a glass container in anindividual section machine). It is sufficient, for instance, to heat asoda-lime-silica glass precursor gel to around 1450° C. for as little as30 minutes to 4 hours to melt the gel into molten glass to the degreedesired. Alternatively, if a lower heating temperature is preferred, thesoda-lime-silica glass precursor gel can be heated to around 1200° C.for 16 hours to 24 hours. Each of these heating options constitutes asignificant energy savings compared to the melting of conventionalsoda-lime-silica glass feedstocks.

The glass precursor gel can be chemically synthesized. By doing so, thethree rate-limiting steps of conventional glass making—dissolution ofquartz sand, bubble removal, and homogenization/mixing of the primaryconstituent oxides—are accomplished at low temperatures by way ofchemical reactions, not the standard procedure in which crystalline rawmaterials (and optionally some cullet) are physically mixed, melted, andmaintained in a molten state to facilitate dissolution. Specifically,the glass precursor gel can be chemically synthesized at temperaturesbelow 300° C., which is well below the melting point of quartz sand.And, once formed, the glass precursor gel can be melted into moltenglass, which can then be formed into a glass product such as, forexample, a glass container or flat glass or tableware, to name but afew. Such melting of the glass precursor gel can be attained morequickly than conventional glass feedstocks because the chemicalsynthesis of the homogeneously chemically mixed gel is conducted throughchemical reactions outside of the glass furnace or other apparatus priorto melting. The low-temperature pre-melting chemical synthesis of thegel can ultimately lower the furnace energy consumption and reduce theinfrastructure and furnace footprint attributed to each glass productproduced.

The glass precursor gel can be chemically synthesized, as will befurther described and demonstrated below in the context of asoda-lime-silica precursor gel, by precipitating the gel from a solublealkali silicate. In general, a silicate solution containing the solublealkali silicate is first prepared. One way to prepare the silicatesolution, for example, is to hydrothermally dissolve quartz sand in acaustic aqueous alkali-based solvent. The ratio of SiO₂ to the alkalioxide in the alkali silicate can be adjusted in solution as needed.Next, the alkali silicate is precipitated out of solution with analkaline earth salt to provide a wet precipitate that, by design, hasthe same proportions of the primary constituent oxides as the desiredend-use glass composition. And finally, solvent may be removed from thewet precipitate to derive the glass precursor gel.

The glass precursor gel can be used to make a glass product as showndiagrammatically in FIG. 1. There, the method of making a glass productis illustrated, and described in the corresponding text, specifically inthe context of using one type of the glass precursor gel-namely, asoda-lime-silica (“SLS”) glass precursor gel. The method is identifiedby reference numeral 10 and includes the following steps: obtaining theSLS glass precursor gel (step 12); melting the SLS glass precursor gelinto molten glass (step 14); and forming the molten glass into a glassproduct (step 16). The method is preferably used to form glasscontainers such as bottles and jars. These types of containers mayinclude a glass body that defines an interior for holding some content.The interior is typically accessible from a mouth that is located at oneaxial end of the glass body. The mouth may be constructed to receive acap or lid. Other types of glass products may of course be made from theSLS glass precursor gel besides containers. While the method shown anddescribed with reference to FIG. 1 is focused on the preparation and useof a SLS glass precursor gel, those skilled in the art will know andunderstand how to adapt the following teachings to other types of glassprecursor gels such as gels composed to produce, for example,borosilicate glass or lead sealing glass.

The SLS glass precursor gel is comprised of a bulk amorphous oxide-basedmatrix that includes at least silica (SiO₂), sodium oxide (Na₂O), andcalcium oxide (CaO) as the primary constituent oxides, andchemically-entrained water as the extending swelling agent. Theamorphous oxide-based matrix of the SLS glass precursor gel, forexample, preferably comprises 60 mol % to 85 mol % silica, 8 mol % to 18mol % sodium oxide, and 5 mol % to 15 mol % calcium oxide. The amorphousoxide-based matrix may also optionally include up to about 10 mol %combined of aluminum oxide, magnesium oxide (MgO), and/or potassiumoxide (K₂O) as additional primary constituent oxides, and any of theother secondary materials recited above including other glass-networkformers, colorants such as iron oxide (Fe₂O₃), other agents (e.g.,oxidizers, reducers, fining agents, etc.), and impurities common in theglass industry. Moreover, as described above, water ischemically-entrained within the amorphous oxide-based matrix such that,when the gel is heated at a rate of 5° C. per minute starting from STP(1 atm pressure and 20° C.), water vapor continues to evolve above 125°C. and up to 400° C., and may even retain as much as 0.5 wt. % water at400° C. The SLS glass precursor gel is porous and friable, having adensity of less than about 2.0 g/cm³ and a surface area greater thanabout 20 m²/g, as described above, and the components that make up theamorphous oxide-based matrix are already homogenously chemically mixedprior to being melted in step 14.

The SLS glass precursor gel can be obtained in step 12 in numerous ways.In one embodiment, as depicted here in FIG. 1, the SLS glass precursorgel is obtained by (1) providing a silicate solution that includes adissolved sodium silicate (step 12 a); (2) adding a soluble calcium saltto the silicate solution to derive a wet precipitate that has sameproportions of the primary constituent oxides as the amorphousoxide-based matrix of the SLS glass precursor gel (step 12 b); and (3)deriving the SLS glass precursor gel from the wet precipitate (step 12c). A specific implementation of steps 12 a-12 c will be described belowin more detail. It should be understood, however, that the SLS glassprecursor gel can also be obtained through other mechanisms notexpressly described, but nonetheless known to skilled artisans,including alternative ways to provide the silicate solution in step 12 asuch as by purchasing the silicate solution or chemically preparing thesolution by melting a mixture of quartz sand and soda ash and thendissolving the resultant product in water.

The silicate solution can be provided in step 12 a by hydrothermallydissolving quartz sand in a caustic aqueous sodium-based solvent. Thecaustic aqueous sodium-based solvent may be a strong sodium base, suchas sodium hydroxide (NaOH), which is preferably concentrated to greaterthan 10 wt. % (of the sodium base) so as to make dissolution of thequartz sand easier. One example of a suitable strong sodium base is 18wt. % NaOH. The hydrothermal dissolution of quartz sand may beaccomplished in a pressure vessel at a pressure above atmosphericpressure. There, the quartz sand may be dissolved in the caustic aqueoussodium-based solvent at a temperature between about 25° C. and about300° C. including all ranges and sub-ranges therebetween, preferablybetween about 200° C. and about 300° C., and a pressure of about 10atmospheres to about 100 atmospheres including all ranges and sub-rangestherebetween, preferably about 30 atmospheres to about 50 atmospheres,over the course of about 3 hours to about 24 hours including all rangesand sub-ranges therebetween. The silicate solution formed under thesehydrothermal conditions contains a dissolved solids phase of sodiumsilicate. The dissolved sodium silicate produced has the generalchemical formula Na₂OxSiO2 with x ranging from 1.5 to 3.75 includingall ranges and sub-ranges therebetween.

The ratio of Na₂O to SiO₂ in the dissolved sodium silicate may have tobe adjusted to ensure the amorphous oxide-based matrix of the SLS glassprecursor gel has the proper mole percentages of silica, sodium oxide,and calcium oxide. In particular, the mole percent proportions of theprimary constituent oxides listed above can be met when the amorphousoxide-based matrix has a molar ratio of Na₂O:CaO:SiO₂ of approximately1:1:6 with variances between 0.8:0.8:6 and 1.4:1.3:6 being acceptablefor typical container glass. The dissolved sodium silicate in thesilicate solution, however, typically includes 2-3 moles of Na₂O forevery 6 moles of SiO₂. To adjust the molar ratio of Na₂O to SiO₂, ifnecessary, a multiple-step technique may be employed. First, the molarratio of Na₂O to SiO₂ in the dissolved sodium silicate may be reducedwith an acid. Nitric acid (HNO₃), for example, can be added to thesilicate solution in a quantity that neutralizes some of the Na₂O tobring the molar ratio of Na₂O to SiO₂ in the dissolved sodium silicatedown to approximately 2:6. Nitric acid neutralizes sodium silicate intosilicic acid (SiH₄O₄) and sodium nitrate (NaNO₃). A further reduction ofthe molar ratio of Na₂O to SiO₂—down to approximately 1:6—is achieved instep 12(b) when, as will be explained in more detail below, sodium isdisplaced by calcium.

Other primary constituent oxides and secondary materials that may bedesired in the amorphous oxide-based matrix of the SLS glass precursorgel may be added into the silicate solution during step 12 a as a solidor they may be dissolved in water prior to their addition into thesolution. Some other materials that may be added into the silicatesolution include aluminum oxide, magnesium oxide, potassium oxide, ironoxide, titanium oxide, zirconium oxide, barium oxide, strontium oxide(SrO), sulfur trioxide (SO₃), and oxides of selenium, cobalt, chromium,manganese, and lead. Aluminum oxide, in particular, which enhances thechemical durability of soda-lime-silica glass and reduces the tendencyof devitrification in the molten glass, may be introduced by adding analumina-bearing mineral to the caustic aqueous sodium-based solventalong with quartz sand under hydrothermal conditions. Adding thealumina-bearing material at this time results in aluminum oxide beingchemically integrated into the dissolved sodium silicate duringhydrothermal dissolution of the quartz sand. Some examples ofalumina-bearing minerals that may be used here are nepheline syenite,aplite, and calumite slag. The aluminum oxide may also be introducedinto the silicate solution in the form of dissolved sodium aluminate.

The list of secondary materials that may be introduced into the silicatesolution during step 12 a is more extensive than those just mentioned.Colorants and decolorants may be added such as one or more of ironoxides (e.g., FeO and/or Fe₂O₃), chromium oxides (e.g., CrO or Cr₂O₃),cobalt oxides (e.g., CoO or Co₂O₃), nickel, copper, selenium, manganesedioxide, cerium oxide, titanium, and a combination of sulfur, iron, andcarbon. Another class of secondary materials that can be added to thesilicate solution is fining agents such as, for example, the combinationof sodium sulfate (Na₂SO₄), carbon, arsenic oxide, and antimony oxide.Still further, oxidizers or reducers can be added to the silicatesolution to modify, if desired, the redox number of the molten glassderived from the SLS glass precursor gel. Examples of common oxidizersand reducers include calcium sulfate (CaSO₄), sodium nitrate (NaNO₃),potassium nitrate (KNO₃), iron pyrite (FeS₂), and graphite.

After the silicate solution has been formulated in step 12 a, thesoluble calcium salt may be added to the silicate solution in step 12 bto derive a wet precipitate that has same proportions of the primaryconstituent oxides (e.g., silica, sodium, and calcium) desired in theamorphous oxide-based matrix of the SLS glass precursor gel. This stepinvolves adding the soluble calcium salt to the silicate solution in anamount that brings the molar ratio of Na₂O:CaO:SiO₂ in the wetprecipitate to approximately 1:1:6, which is the desired molar ratio ofthe amorphous oxide-based matrix and, in turn, the soda-lime-silicaglass produced from the SLS glass precursor gel. The soluble calciumsalt may include, for example, calcium nitrate (Ca(NO₃)₂), calciumchloride (CaCl₂), calcium hydroxide (Ca(OH)₂) or any other solublecalcium salt or combination of soluble salts that provides a source ofcalcium ions. When added to the silicate solution, the calcium ionsprovided by the soluble calcium salt displace sodium in the dissolvedsodium silicate, thus introducing calcium oxide into the silicate, whichcauses the newly-modified sodium silicate to precipitate out of solutionas the wet precipitate. And since every 1 mole of calcium ions (whichresults in a corresponding mol of CaO) displaces 1 mole of Na₂O in thedissolved sodium silicate, the amount of the soluble calcium salt thatneeds to be added to the silicate solution to provide the wetprecipitate with the 1:1:6 molar ratio of NazO:CaO:SiO₂ can be easilycalculated based on the molar ratio of Na₂O:SiO₂ in the silicatesolution from step 12 a.

The displacement of Na₂O with CaO, and the precipitation of the wetprecipitate, is preferably carried out with the silicate solution beingas concentrated as possible. It has been found, in fact, that as thedissolved sodium silicate becomes more dilute in the silicate solution,the amount of Na₂O in the wet precipitate decreases while the amounts ofSiO₂ and CaO are not similarly affected. This, in turn, can increase therespective mole percentages of SiO₂ and CaO in the wet precipitate,potentially beyond what is acceptable, due to the isolated loss of Na₂O.The potential for the unintended loss of Na₂O during step 12 b can thusbe countered by performing step 12 with a concentrated silicatesolution. A suitably concentrated silicate solution may comprise atleast 5 wt. % sodium silicate at the end of step 12 a and, morepreferably, between 25 wt. % and 40 wt. % sodium silicate at the end ofstep 12 a.

The phenomenon of isolated Na₂O loss from the wet precipitate based onthe concentration of the silicate solution has been demonstrated in asimple experiment. Specifically, four separate samples of 281 grams ofSTAR-grade sodium silicate were diluted with 0 L, 1 L, 2 L, and 3 L ofwater. Each solution of the sodium silicate was then precipitated with34.5 grams of calcium nitrate dissolved in 500 mL of water. An SLS glassprecursor gel was obtained from each sample, melted and formed intoglass, polished, and then analyzed with x-ray fluorescence to determineits glass chemistry composition. Assuming 100% ion exchange efficiencybetween Na and Ca, the nominal composition of the four samples of glassreported as mol % fractions of the total primary constituent oxidesshould be about 72.2 mol % SiO₂, 15.8 mol % Na₂O, and 12.0 mol % CaO.But, as shown below in table 2, the Na₂O mole percentage of the glass(and thus the amorphous oxide-based matrix of the SLS glass precursorgel that formed the glass) began to decrease as the dissolved sodiumsilicate became more dilute prior to precipitation with calcium nitrate,while the undiluted sample retained nearly all of the Na₂O.

TABLE 2 Effects of Dilution on Sodium Oxide Content Composition (mol %)as a fraction of the total primary glass-forming oxides SiO₂ Na₂O CaONominal 72.1 15.9 12.0 Sodium 0 70.4 15.7 12.5 Silicate 1 72.0 14.1 12.3Dilution (L) 2 72.3 10.3 15.6 3 72.8 8.9 16.5

The SLS glass precursor gel can be derived from the wet precipitate instep 12 c by removing the liquid solvent. Removal of the liquid solventcan be achieved by any number of separation techniques. Centrifugation,membrane osmosis, filter press, screw press, chemical separation, and/ormechanical compounding (i.e., squeezing) are notable examples of ways toseparate the liquid solvent from the wet precipitate. The remainingsolids-which have been chemically prepared in steps 12 a and 12 b tohave the desired glass chemistry formulation of soda-lime-silicaglass—may then be dried. Drying can be performed in a convection oven atmoderate temperatures of about 100° C. to about 500° C., for example, orit can be performed in any other suitable manner at conditionssufficient to extract residual solvent from the recovered solids.Rinsing of the recovered solids between solvent removal and drying mayoptionally be performed to wash away any reactants and/or reactionbyproducts. When the liquid solvent has been satisfactorily removed, theSLS glass precursor gel remains, and at this point the gel is ready tobe used as a feedstock for making glass products according to steps 14and 16.

The SLS glass precursor gel is melted into molten glass in step 14. Themelting of the SLS glass precursor gel can be accomplished relativelyquickly compared to conventional soda-lime-silica glass feedstocksbecause the amorphous oxide-based matrix of the gel does not includelarge amounts of crystalline materials (e.g., quartz sand) orcarbonate-containing materials, and it has already been chemicallyhomogenized to the desired glass formulation before melting. In oneembodiment, to melt the SLS glass precursor gel into molten glass thatis suitable for subsequent glass forming operations, the gel needs onlyto be heated at a temperature of about 1450° C. or greater for a timeperiod of about 30 minutes to about 4 hours including all ranges andsub-ranges therebetween. Such a heating time is about one-sixth or lessthan the time it takes to satisfactorily melt conventional glassfeedstocks. Longer heating times may of course be practiced, if desired,but they generally are not required. As an example of a longer heatingtime, the SLS glass precursor gel may be heated to 1200° C. for about 16hours to about 24 hours, which still produces a homogeneous, bubble-freemelt yet consumes less energy than melting conventional soda-lime-silicaglass feedstocks.

The SLS glass precursor gel can be melted in a glass furnace. Forexample, the glass furnace may be a refractory brick-line vessel that isconstructed with gas combustion and thermal radiation heat sources toheat the interior of the vessel. In use, the SLS glass precursor gel maybe introduced into the furnace and on top of a glass bath from a sidedoghouse. The heat sources heat the SLS glass precursor gel from the topand/or bottom and the glass bath heats the floating gel from the bottom.The SLS glass precursor gel eventually melts and assimilates as moltenglass into the glass bath. This occurs rather quickly for the SLS glassprecursor gel, as compared to conventional soda-lime-silica glassfeedstocks, because quartz sand dissolution, bubble removal, andhomogenization of the molten glass derived from the SLS glass precursorgel has already been accomplished by low-temperature chemical reactions.As such, the molten glass derived from the SLS glass precursor gel doesnot have to stay in the furnace in a melted state for very long beforeit is ready for subsequent formation into a glass product, as indicatedby the heat cycle times and temperatures recited above. For this reason,furnaces for melting the SLS glass precursor gel may be designed to bemuch smaller than traditional glass melting furnaces.

Forming the molten glass derived from the SLS glass precursor glass intoa glass product at step 16 can be carried out by any suitable glassforming process. To make a glass container, for instance, the moltenglass may be thermally conditioned (step 16 a), delivered into a sectionmachine (step 16 b), and then fashioned into a glass container (step 16c) of the desired size and shape. The molten glass is preferablythermally conditioned in a forehearth, which is constructed to receivethe molten glass from the glass furnace. The forehearth may includeheated channels that reduce the temperature of the molten glass down toabout 1050° C. to about 1200° C., including all ranges and sub-rangestherebetween, so that the molten glass achieves the desired thermalprofile and viscosity for subsequent forming. At the end of theforehearth, a shearing blade may cut off a precise portion of the moltenglass, known as a glass gob, which in turn may be delivered by a gobdelivery system into a blank mold of the section machine. The sectionmachine, which is preferably an individual section (IS) machine, thenfashions the gob into a glass container by the blow-and-blow method, thepress-and-blow method, or some other method.

The SLS glass precursor gel has a tendency to produce soda-lime-silicaglass with good clarity and color as opposed to the blue/green colorthat is typically found in soda-lime-silica glass derived fromconventional glass feedstocks. The blue/green color, which is attributedto iron impurity, is caused by the reduced state of iron (ferrous,Fe²⁺), which has a broad absorption peak from 600 nm to 1500 nm.Oxidizing the ferrous iron to ferric iron (Fe³⁺) reduces the perceivedblue/green coloration of the soda-lime-silica glass since ferric iron isa much weaker colorant that ferrous iron. Such oxidation of any ironcontent from ferrous to ferric is thought to occur when melting the SLSglass precursor gel in step 14, thus leading to clearer glass. Withoutbeing bound by theory, it is currently believed that the SLS glassprecursor gel retains some of the soluble sodium byproduct that isgenerated when Na₂O is displaced with CaO in step 12 b. The sodiumbyproduct, believed to be sodium nitrate (Na(NO₃)₂), is a knownoxidizing agent because, when heated, the nitrate decomposes to generateoxygen (O₂), nitric oxide (NO), and nitrogen dioxide (NO₂). Oxygen gashas been shown to evolve from the SLS glass precursor gel between about450° C. and about 1500° C. when the gel is heated.

FIG. 3 is helpful in quantifying the tendency of the SLS glass precursorgel to produce flint glass without the blue/green tint. There, thetransmittance profile of three samples of soda-lime-silica glass isdepicted: two commercial samples produced from virgin crystalline rawmaterials and one sample produced from the SLS glass precursor gel. Theiron content expressed as wt. % Fe₂O₃ (not a metric of the Fe²⁺/Fe³⁺ratio) of the two samples produced from crystalline raw materials(samples A and B) and the sample produced from the SLS glass precursorgel (sample C) were measured by x-ray fluorescence and are set forth intable 3 below.

TABLE 3 Iron Content of Samples Expressed as wt. % Fe₂O₃ Sample GlassSource wt. % Fe₂O₃ A Conventional Crystalline Raw Materials 0.016 BConventional Crystalline Raw Materials 0.041 C SLS Precursor Gel 0.042As shown in the table above and the graph in FIG. 3, thesoda-lime-silica glass obtained from the SLS glass precursor gel, whichhas 0.042 wt. % iron as Fe₂O₃, is akin to flint glass derived fromconventional crystalline raw materials that has 0.016 wt. % iron asFe₂O₃ in the 600-1200 nm spectral range. The suppression of Fe²⁺absorption in the glass obtained from the SLS glass precursor gel(sample C), again, is thought to be caused by residual sodium nitratethat is either trapped in the pores of the amorphous oxide-based matrixof the SLS glass precursor gel or chemically bound to the amorphousoxide-based matrix, despite the repeated separation, rinsing, and dryingsteps that may be carried out in step 12 c.

The glass container may then be subject to additional manufacturingand/or handling after being formed in the section machine. Specifically,once the glass container emerges from the section machine, it may becooled to preserve its shape, followed by re-heating in one or moreannealing lehrs. The glass container may be re-heated (or annealed) inthe annealing lehr(s), usually at a temperature between about 550° C.and about 600° C. for about 30 minutes to about 90 minutes, to removestress points in the container. The glass container may then be cooledgradually. Any of a variety of hot-end, cold-end, antireflective,scratch-resistant, and/or glass strengthening coatings may be applied tothe exterior surface of the glass container before the container isinspected and packaged.

The above discussion related to the glass precursor gel, althoughspecifically directed to the preparation and use of a soda-lime-silicaglass precursor gel, can nonetheless be adapted to prepare and use aglass precursor gel in other contexts, most notably the preparation anduse of a glass precursor gel to make borosilicate glass or lead sealingglass. For each of borosilicate glass and lead sealing glass, thechemical synthesis of the glass precursor gel (step 12) is essentiallythe same, with the only significant difference being the way in whichthe composition of the dissolved alkali silicate is manipulated insolution and during precipitation. For example, to make borosilicateglass, boric acid could be added to the silicate solution to acidify thesolution below the solubility limit of the silicate (below a pH of about9.5-10) so that the wet precipitate, and thus the amorphous oxide-basedmatrix of the glass precursor gel, that eventfully results willincorporate B₂O₃. As another example, to make lead sealing glass, asoluble lead salt, such as lead nitrate, could be added to the silicatesolution (in lieu of the soluble calcium salt) to incorporate PbO intothe wet precipitate and, therefore, the amorphous oxide-based matrix ofthe glass precursor gel.

EXAMPLES

The following Examples demonstrate specific embodiments of the glassprecursor gel, in particular a SLS precursor gel and methods of theirmanufacture, in accordance with the present disclosure.

Example 1

This example describes one way in which approximately 100 grams of theSLS glass precursor gel has been obtained. To begin, a silicate solutionwas purchased from PQ Corporation (Corporate headquarters in Malvern,Pa.). The silicate solution contained Na₂OxSiO2, with x being 2.58, asa dissolved solids phase that was present at 37.1 wt. % in solution. 281grams of the silicate solution was used without further dilution. Next,5.75 grams of 15.5 M nitric acid was added to approximately 200 mL ofdeionized water, and the entire contents were then added to the silicatesolution with vigorous stirring. The nitric acid was added to neutralizesome of the sodium oxide content of the dissolved sodium silicate. Afterthat, 20.6 grams of limestone (calcium carbonate) was dissolved inapproximately 500 mL of deionized water with a stoichiometric amount of15.5 M nitric acid (−37.2 grams) to convert the limestone into solublecalcium nitrate. Carbon dioxide was released at that time. The calciumnitrate solution was then added to the silicate solution with vigorousstirring at room temperature. A white wet precipitate formedimmediately.

The silicate solution with precipitate was placed in plastic tubes andcentrifuged for approximately 5 minutes to sediment the wet precipitate.The supernatant was then decanted and replaced with deionized water torinse the wet precipitate. The centrifugation and rinsing procedureswere repeated two more times and, after the last decanting step, noadditional deionized water was added to the test tube. At that point thewet precipitate was spread on a dish and dried in a convection oven at120° C. overnight. After drying, a SLS glass precursor gel was obtainedin the form of brittle, chalky, white chunks that had a chemicallyhomogenized chemical formulation. The SLS glass precursor gel was thenmelted in a platinum crucible at 1450° C. The SLS glass precursor gelwas fully melted and bubble-free after 30 minutes. Additional melting ofa similarly-formed SLS glass precursor gel was carried out at lowertemperatures—specifically, 1200° C. and 1350° C.—and was found to befully melted and bubble-free after 16 hours in each instance.

The target mole percentages of certain materials in the molten glassproduced by the SLS glass precursor gel of this example are reported intable 4 below as “Reference 1.” As can be seen, the target molepercentages of SiO₂, Na₂O, and CaO were 74.0, 13.6, and 12.4respectively. The SLS glass precursor gel, in actuality, produced moltenglass that contained weight percentages of SiO₂, Na₂O, and CaO thatclosely approached the target weight percentages of those primaryconstituent oxides. The SLS glass precursor gel can repeatedly achievethese compositions of the primary constituent oxides with less than a 1mol % fluctuation in Na₂O (i.e., target Na₂O±1.0 mol %).

Example 2

In this example, the silicate solution was made from quartz sand insteadof being purchased as in example 1. To begin, 374 grams of quartz sandwas added to a 5.7 M NaOH solvent. This mixture was placed in a stirredautoclave reaction vessel and reacted for 12 hours at 250° C. Over 99.9mol % of the quartz sand was dissolved. The resulting silicate solutioncontained dissolved sodium silicate having the chemical formulaNa₂OxSiO2 with x being about 2.6. An SLS glass precursor gel wasultimately made using the silicate solution in the same manner set forthin example 1. It also melted in the same way with the same results. Themole percentages of certain materials in the molten glass produced bythe SLS glass precursor gel of this example are reported below in table4.

Example 3

In this example, aluminum oxide was introduced into the silicatesolution and, ultimately, the SLS glass precursor gel. Here, when makingthe silicate solution, 853 grams of water, 218 grams of NaOH, 321 gramsof quartz sand, and 29 grams of nepheline syenite were mixed in astirred autoclave reaction vessel. The mixture was reacted for 10 hoursat 250° C. and was prepared with a target molar ratio of Na₂O to SiO₂ of1:2. After the hydrothermal treatment, the resultant silicate solutionwas filtered through #40 Whatman paper. It was found that 6.3 wt. % ofthe original solids did not dissolve. And since the nepheline syeniteaccounted for 8.3 wt. % of the original solids, it was believed that atleast some of the nepheline syenite dissolved into the silicatesolution. The filtered silicate solution was then used to make a SLSglass precursor gel as set forth in example 1 with the adjustment ofmore nitric acid to compensate for the greater molar ratio of Na₂O toSiO₂ in the dissolved sodium silicate. The molten glass produced by theSLS glass precursor gel of this example was found to contain about 0.5%Al₂O₃. The mole percentages of Al₂O₃ and other materials in the moltenglass are reported below in table 4.

Example 4

This example describes yet another way to introduce aluminum oxide intothe silicate solution and, ultimately, the SLS glass precursor gel.Here, the SLS glass precursor gel was prepared in the same way as inexample 1, except that aluminum hydroxide was dispersed in the nitricacid used to neutralize some of the Na₂O. The aluminum hydroxide did notfully dissolve in the silicate solution. After the SLS glass precursorgel was made using the silicate solution, and upon being heated, theresidual aluminum hydroxide converted to alumina with the release ofwater. And after only 15 minutes of melting the SLS glass precursor gelat 1450° C., there were no alumina stones observed in the glass melt,even though alumina is a refractory material. The molten glass producedby SLS glass precursor gel of this example was found to contain about1.0 mol % Al₂O₃ as is reported below in table 4 along with the molepercentages of other materials in the molten glass.

Example 5

The SLS glass precursor gel was prepared here as described in example 1with a few modifications. First, to introduce aluminum oxide into thesilicate solution and the SLS glass precursor gel, the amount of sodiumaluminate needed to yield 1.0 mol % Al₂O₃ in the dissolved sodiumsilicate was dissolved in water and mixed with the silicate solutionrecited in example 1. Second, a blend of calcium nitrate and magnesiumnitrate was used to precipitate the dissolved sodium silicate into thewet precipitate with the intent of adding a small amount of MgO alongwith CaO. The amounts of Al₂O₃ and MgO sought to be added to the moltenglass produced by the SLS glass precursor gel in this example arereported in table 4 below as “Reference 2.” The molten glass produced bymelting the SLS glass precursor gel was found to contain about 0.9 mol %and 2.7 mol % of Al₂O₃ and MgO, respectively, which is also reportedbelow in table 4 along with the mole percentages of other materials inthe molten glass.

Example 6

The SLS glass precursor gel in this example was prepared as described inexample 1 except that cobalt oxide (CoO) and chromium(III) oxide (Cr₂O₃)were added to the silicate solution before precipitation with thecalcium nitrate. These oxides did not dissolve, but were insteaddispersed in the silicate solution with vigorous mixing beforeprecipitation. The cobalt oxide and chromium(III) oxide were added tothe silicate solution in amounts needed to achieve 25 ppm and 1 ppm,respectively, in the wet precipitate. The SLS glass precursor gel thatwas made using the silicate solution looked the same as the SLS glassprecursor gel of example 1. After heating the SLS glass precursor gel ofthis example for 5 minutes at 1450° C., however, a chemicallyhomogeneous and dark blue molten glass was attained that did not haveany stones or streaks of color. Furthermore, after continued heating at1450° C. for 1 hour, the molten glass was free of bubbles.

Example 7

The SLS glass precursor gel in this example was prepared as described inexample 1 except that Fe₂O₃, carbon, and sulfate anions were added tothe SLS glass precursor gel. Fe₂O₃ and carbon were added as insolublecompounds prior to precipitation of the dissolved sodium silicate. Thesulfate anions were added to the wet precipitate in the form of sulfuricacid after the final rinsing step and before drying. Adding the sulfateanions (via sulfuric acid) at this time was done because sodium sulfatewould have been easily rinsed away during the rinsing steps. The SLSglass precursor gel made in this example, when melted, produced moltenglass having an aquamarine blue color, which was somewhat out of theordinary since the added compounds employed here typically produce anamber/brown color. The aquamarine blue color observed here suggests thatthe iron/sulfur complex experienced a more oxidizing environment thanwhat would normally be found in conventional molten glass derived fromcrystalline raw materials. This belief is consistent with thetransmission data for clear soda-lime-silica glass shown in FIG. 3 andthe belief that an oxidizing environment arises on account of residualsodium nitrate byproducts left over in the SLS glass precursor gel.

Example 8

In this example, the SLS glass precursor gel was prepared as describedin example 7 except that that amount of carbon added was increased.Because carbon is a reducing agent, the increase in added carbon wasintended to overcome the oxidizing environment apparently attributed toresidual sodium nitrate byproducts in the SLS glass precursor gel. Themolten glass that resulted from melting the SLS glass precursor gel ofthis example was brown in color.

TABLE 4 Compositions of Melted Glass as Measured by X-Ray FluorescenceGlass Composition in mol % SiO₂ Na₂O CaO MgO Al₂O₃ Example 1 72.5 13.812.4 1.2 0.1 Example 2 72.1 13.3 13.0 1.5 0.1 Example 3 72.3 12.3 13.41.5 0.5 Example 4 71.7 14.0 11.9 1.4 1.0 Example 5 71.2 12.8 12.4 2.70.9 Reference 1 74.0 13.6 12.4 0 0 Reference 2 72.2 13.0 11.2 2.5 1.0

There thus has been disclosed a glass precursor gel that fully satisfiesone or more of the objects and aims previously set forth. The disclosurehas been presented in conjunction with several illustrative embodiments,and additional modifications and variations have been discussed. Othermodifications and variations readily will suggest themselves to personsof ordinary skill in the art in view of the foregoing discussion. Forexample, the subject matter of each of the embodiments is herebyincorporated by reference into each of the other embodiments, forexpedience. The disclosure is intended to embrace all such modificationsand variations as fall within the spirit and broad scope of the appendedclaims.

1. A glass precursor gel comprising: a bulk amorphous oxide-based matrixhaving an inorganic network of primary constituent oxides, the primaryconstituent oxides comprising 30 mol % to 90 mol % silica and one ormore of the following: (A) 0.1 mol % to 25 mol % of one or more alkalioxides in sum total, (B) 0.1 mol % to 25 mol % of one or more alkalineearth oxides in sum total, (C) 1 mol % to 20 mol % boric oxide, (D) 5mol % to 80 mol % lead oxide, or (E) 0.1 mol % to 10 mol % aluminumoxide; wherein the bulk amorphous oxide-based matrix is homogenouslychemically to mixed and, further, wherein the glass precursor gel has adensity of less than 2.0 g/cm³.
 2. The glass precursor gel set forth inclaim 1, wherein the primary constituent oxides are silica, sodiumoxide, and calcium oxide.
 3. The glass precursor material set forth inclaim 2, wherein the amorphous oxide-based matrix comprises 60 mol % to85% silica, 8 mol % to 18 mol % sodium oxide, and 5 mol % to 15 mol %calcium oxide.
 4. The glass precursor gel set forth in claim 3, whereinthe amorphous oxide-based matrix further comprises aluminum oxide. 5.The glass precursor gel set forth in claim 1, wherein the amorphousoxide-based matrix further comprises at least one of glass networkformers, coloring agents, redox agents, or combinations thereof.
 6. Theglass precursor gel set forth in claim 1, wherein the glass precursorgel has a density of 1.6 g/cm³ to 1.85 g/cm³ and a surface area of atleast 20 m²/g as measured by nitrogen BET adsorption.
 7. The glassprecursor gel set forth in claim 1, wherein, upon heating, the glassprecursor gel evolves oxygen gas between 450° C. and 1500° C.
 8. Theglass precursor gel set forth in claim 1, further comprising water thatis chemically entrained within the bulk amorphous oxide-based matrix. 9.A method of making a glass product, the method comprising: obtaining aglass precursor gel that comprises a homogeneously chemically mixed bulkamorphous oxide-based matrix and an extending swelling agent, the bulkamorphous oxide-based matrix having an inorganic network of primaryconstituent oxides, the primary glass-forming constituent oxidescomprising 30 mol % to 90 mol % silica and one or more of the following:(A) 0.1 mol % to 25 mol % of one or more alkaline earth oxides in sumtotal, (B) 0.1 mol % to 25 mol % of one or more alkaline earth oxides insum total, (C) 1 mol % to 20 mol % boric oxide, (D) 5 mol % to 80 mol %lead oxide, or (E) 0.1 mol % to 10 mol % aluminum oxide; melting theglass precursor gel into molten glass; and forming the molten glass intoa glass product.
 10. The method set forth in claim 9, wherein the stepof obtaining the glass precursor gel comprises: providing a silicatesolution that includes a dissolved alkali silicate, the dissolved alkalisilicate having a molar ratio of an alkali metal oxide to silica; addingan alkaline earth salt to the silicate solution to displace some of thealkali oxide with an alkaline earth metal oxide and to derive a wetprecipitate having a molar ratio of the alkali metal oxide to thealkaline earth metal oxide to silica; and removing liquid solvent fromthe wet precipitate to obtain the glass precursor gel.
 11. The methodset forth in claim 10, further comprising: adjusting the molar ratio ofthe alkali oxide to silica in the dissolved alkali silicate byneutralizing some of the alkali oxide with an acid such that the molarratio of the alkali oxide to silica is reduced.
 12. The method set forthin claim 9, wherein the molar ratio of the alkali oxide to the alkalineearth oxide to silica is between 0.8:0.8:6 and 1.4:1.3:6.
 13. The methodset forth in claim 9, wherein the step of melting the glass precursorgel is performed at 1200° C. to 1450° C. for a period of 30 minutes to16 hours.
 14. A method of making a glass product, the method comprising:providing a silicate solution that includes a dissolved sodium silicate,the dissolved sodium silicate comprising a molar ratio of Na₂O:SiO₂;adding a soluble calcium salt to the silicate solution to displace someof the sodium oxide in the dissolved sodium silicate with calcium oxideand to derive a wet precipitate that comprises a molar ratio ofNa₂O:CaO:SiO₂; removing solvent from the wet precipitate to obtain asoda-lime-silica glass precursor gel, the gel comprising a bulkamorphous oxide-based matrix having an inorganic network of oxides thatcomprises 60 mol % to 85 mol % silica, 8 mol % to 18 mol % sodium oxide,and 5 mol % to 15 mol % calcium oxide; melting the soda-lime-silicaglass precursor gel into molten glass; and forming the molten glass intoa glass product.
 15. The method set forth in claim 14, wherein providingthe silicate solution comprises dissolving quartz sand in a sodium-basedsolvent at a temperature between 25° C. and 300° C. and a pressure of 10atmospheres to 100 atmospheres for 3 hours to 24 hours.
 16. The methodset forth in claim 14, further comprising: adjusting the molar ratio ofNa₂O:SiO₂ in the dissolved sodium silicate by neutralizing some of thesodium oxide with an acid such that the molar ratio of Na₂O:SiO₂ isreduced.
 17. The method set forth in claim 16, wherein the step ofadding a soluble calcium salt includes displacing sodium oxide in thedissolved sodium silicate with calcium oxide such that the molar ratioof Na₂O:CaO:SiO₂ in the wet precipitate is between 0.8:0.8:6 and1.4:1.3:6.
 18. The method set forth in claim 14, wherein forming themolten glass into a glass product comprises: thermally conditioning themolten glass at a temperature of about 1050° C. to about 1200° C. afterthe molten glass has been removed from the furnace; delivering a gob ofthe molten glass to an individual section machine; and forming themolten glass into a glass container in the individual section machine,the glass container having a glass body defining an interior accessibleat a mouth located at one axial end of the glass body.
 19. The methodset forth in claim 14, wherein the soluble calcium salt includes atleast one of calcium nitrate, calcium chloride, or calcium hydroxide.20. The method set forth in claim 14, wherein the silicate solution isconcentrated to at least 5 wt. % of the dissolved sodium silicate at thetime the soluble calcium salt is added to the silicate solution.
 21. Themethod set forth in claim 14, wherein the step of melting thesoda-lime-silica glass precursor gel evolves oxygen gas between 450° C.and 1500° C.
 22. The method set forth in claim 14, wherein the step ofmelting the soda-lime-silica glass precursor gel does not release carbondioxide gas.
 23. The method set forth in claim 14, wherein the step ofmelting the soda-lime-silica glass precursor gel evolves water vaporabove 125° C.